The objective of this tutorial is to ensure you are able to operate the Shopbot CNC router. Shopbot is one of the simplest CNC machines to setup and run but nevertheless it is paramount take a few key points in consideration with regards to safety. The information provided below is in support of our in-class training sessions. They do not substit
ute proper hands-on training with an experienced operator. They are neither complete nor exhaustive but offer some typical use case precautions. If you have not gone through formal training do not attempt to follow the instructions below on your own.
General Safety Instructions
- If something goes wrong be prepared to use the first aid kit and immediately seek for help. The equipment’s condition if damaged is less important than your health.
- If you have never used the machine before do not attempt to operate it without the instructions of trained person. This tutorial does not substitute the experience of somebody who have used CNC machines extensively.
- For the first 10 machine hours always use the equipment in the presence of another person who is trained in using it. In general it is a good practice to always have have somebody around in case something goes wrong.
- Avoid using machines such as the Shopbot when you are not in a good physical or mental condition. If for whatever reason you cannot focus or concentrate it is not advisable to use such equipment.
- When cutting using the router head always wear the safety goggles. The spindle rotates at about over 10,000 times per minute. Material is chipped off and may reach you even if you are at what you may consider safe distance or protected behind the safety fence.
- Never remove the safety fence from the machine and always place the front cover back before you start cutting. This will prevent debris from fly out of the work envelope of the machine and put a physical barrier between you and the tool.
- Do not put your hands within the work envelope of the machine while it is active / moving. You can pause the machine program to make adjustments. Don’t try to take dangerous shortcuts.
- Do not leave the machine unattended or distract yourself while the Shopbot is running. You need to be always in proximity of the keyboard, mouse or the emergency stop switch. Either pressing the spacebar, any mouse button or the physical red switch will force the machine to immediately halt.
- When changing the machine’s tool bit, always make sure you have tightened the tool collet sufficiently to ensure that the bit will not fly while cutting.
- Never touch the tool bit after cutting is complete. Due to friction the tool gets often pretty hot and you may burn your finger. Let it cool off for a few minutes and then change it.
- Always start with lower cutting speeds (such as 1000mm/min for soft material) and increase progressively after testing iterations. Do not use high speeds especially with hard material and/or small diameter tools. They may break and fly off.
- Do not use very low speed either as accumulated heat due to friction may cause fire hazards when cutting flammable materials such as woods and plastics. Seek the advice for an experienced person.
- Do not take deep cuts with harder materials or small diameter tools as they may break off and fly about. As a conservative rule of the thumb do not cut deeper than the tool’s diameter.
- Do not leave loose objects such as pens, rulers, tools within the work envelope of the machine. Be very careful when using clamps or other positioning contraptions that may collide with the machine head.
- Do not try to cut material that you have not attempted before or without the advice and presence of an expert user. In particular this machine is not made for cutting metals and other hard materials. You may injure yourself, break the equipment or even cause building hazards.
Always visually inspect the machine code file for errors that may cause havoc. In particular, verify the initialization and termination sequence if well clear off the material and machine table. In addition run through the point to point motion list and verify the the Z-values are reasonable. Negative values typically imply cutting through the material stock. If your material is 20mm and you spot Z=-30.0 this means that assuming zero is at the top of material stock, you will be cutting through the stock into the base of the machine.
Startup and Shutdown
The following sequence walks through the steps to turn on and off the machine.
1. Turn on the mains transformer black box connected to the mains. The machine runs on 120V and the mains power supply is 240V. This is the first step in starting the machine and last to turn it off (reverse order).
2. Turn on the machine itself using the red safety switch at the front panel. First lift the red cap and then the secondary switch hidden underneath it. This is the second and second last step to turn on/off the machine.
3. Turn on the desktop computer underneath the workbench and log in using the default user windows credentials. You guessed it this is the third and third last step as far as physical startup/shutdown goes.
4. On the desktop locate the Shopbot 3 application and start it. It will initialize by trying to connect to the machine using the USB connection. If it fails doing so turn off the everything in reverse order and try again.
Jogging is a common term used to denote manual or idle motion operations of CNC / robotic equipment for positioning. In this segment we will look at setting the work XYZ origin point (0,0,0) manually.
1. In the Shopbot control panel click the yellow button to bring up the jogging panel. From here you can move each of the three axes using the arrow buttons. The X-axis of the machine spans from left to right, the Y-axis from front to back and the Z-axis from down to up (when standing in front of the Shopbot).
2. Move the machine head using the arrow keys until you locate a point within your material stock that suit as the origin point. The origin point is arbitrary but typically it set at the lower left corner of the design / material. The idea here is that this point represents the World origin in your CAD file. Setting the origin at the lower left corner of the material assumes that all geometry in the CAD file is within the positive quadrant of the World CS. In addition, you need to keep in mind that the bounding rectangle of all geometry used needs to be physically accessible by the machine as the ranges of the axes are limited to circa 600 x 450 x 100mm.
3. When done selecting the work origin click the zero axes blue button and check all three axes. Notice that the reading in the control panel will all reset to zero. For safety retract the Z-axis upwards (eg. 50mm) such that when a new program initiates the machine head is well clear off the table.
While setting the work origin XY is always done by eyeballing the location of the tool in relationship with the material stock (like with the laser cutter), we can set the Z-axis zero position using an automated process. This operation is meaningful for machining surfaces rather than drawing or engraving. By convention the vertical zero position along the Z-axis is set at the topmost surface of the material stock. This simplifies the process of tracking the machine’s position visually: all negative Z-values imply actually cutting at typically lower speeds and all positive Z-values imply rapid motions between cutting path entry and exit points.
1. Slide the plate out of its socket in the front face of the machine and place it on top about the middle of the material stock. As we cannot assume that the top surface of the stock is absolutely flat and horizontal it makes sense to pick the middle rather than a corner point.
2. Take the alligator clip from the same slot and secure it on the drill bit tool. Note that the way this process works is by sending a current between the tool and the plate which act as a switch to stop the machine when approaching one another. This means that the tool needs to be conductive for this to work (such as most feric tool bits). If you for instance clip the sharpie pen the machine will most likely crash itself and destroy something.
3. Jog the machine until the tool bit is right above the middle of the plate and click the zero Z-axis using the plate button found on the Shopbot software control panel. Follow the instructions and observe how the machine head will move down until the bit touches the plate. After two iteration the bit will retract to 1/2″ above the top of material.
4.Remove the plate and clip and store them in the compartment where you found them at the front panel of the machine.
5. The Z-axis is now automatically set correctly to zero. Do not set the zero value using the jogging panel and don’t be confused that the reading is set to 12.7mm. You can still change the zero point in XY by just checking only the appropriate boxes in the jogging panel.
Drawing using a Sharpie Tool
1. Draw a bounding rectangle with the dimensions equal to your paper size from CAD origin into the positive quadrant of the World CS. This serves a reminder of the physical dimensions of your drawing. Make sure you are working in millimetres.
2. Draw any number of lines/curves in the World XY plane. The geometry may be created by hand, through 3D operations and projection onto the XY plane or procedurally using Grasshopper. Just make sure that all curves are on or above the XY plane otherwise you may crush the pen into the table.
3. Load the Grasshopper converting script and import (select multiple) into the Machine Paths node. You should immediately see on screen the curves highlighted as well as the transfer bridges between curves.
4. You may optionally adjust the conversion resolution from curves to polylines. The default value is 5deg which you may reduce in order to increase the number of points per curve. Using too small error tolerance will create numerous points and very large machine files.
5. Locate and adjust the motion speed slider. Generally, 5000mm/min is relatively fast for drawing using the sharpie pen
6. In the rightmost end of the script right click the machine path yellow panel and copy the data only into the clipboard.
7. Open windows notepad and paste the generated code. In this case, take note that there should not be any negative value (negative means that the tip is pushed downwards into and through the material). Save the file but make sure you have selected custom file extension “*.*” for the drop down instead of “*.txt” and provide a filename of your choice ending with “.sbp”
8. On the machine lift the router head and place the sharpie in the tool socket. The pen needs to be loose enough to be moving up and down pushed by the counterweight inside the brass tubing of the tool holder.
9. Place a piece of paper on the machine bed and stick it with masking tape down. Visually make sure it aligned with the XY axis of the machine and proceed setting the zero/origin using the jogging instructions above.
10. In the shopbot control panel click the start button, select the file and click start. Note that the machine code contains instructions for starting up the spindle, which should be off during this tutorial and can ignored.
Cutting a Foam Mould
Use either the Grasshopper script provided in class or RhinoCAM to generate your Shopbot code file. Additional instructions for setting up RhinoCAM for Shopbot are provided. Prepare such that when ready to cut you have a SBP file ready and do not need to model extensively on the Shopobot workstation.
1. For the purposes of the second assignment please note the following constraints:
- Your cutting time should not exceed 30min. You can check the time either through the RhinoCAM information dialog, the Grasshopper script file or just measure the total length of your machine path and divide by the feed rate speed. Example: 5000mm cutting length / 1000mm/min = 5min cutting time.
- Your cutting speed should not exceed 50mm/sec (~3000mm/min) with lower bound is 16.6mm/sec (1000mm/min). Recommend speed is circa 40mm/sec @ 10,000 RPM. Do not run the spindle higher.
- You cutting depth should not exceed 20mm. Double check your machine code file to verify that no Z coordinate is below -20mm (assuming that zero represents the top of material stock).
2. Obtain a EPS blank from Kah Wee and hot-glue it (or double sticky tape it) onto the bed on the Shopbot. Make sure the surface is clear of dust and verify that the slab is secured on the machine. Place it about the middle of the machine’s bed.
3. Follow the instructions above the initialize Shopobot and zero the workspace coordinates, first the XY point and then Z using the plate. To ensure that will not have flat spots at the top of material make sure that the entire machine path is about a millimetre under the top of the material (as the blank may not be absolutely flat).
4. Close the safety cover panel, turn on the spindle switch (pull up the red button on the router head itself) and switch on the router function with the key (slot under the red switch on the front panel of the Shopbot). Plug the vacuum cleaner nozzle onto the attachment point on the router head and turn on the dust collection.
5. Proceed with the general instructions for cutting as seen above and make sure you follow the safety procedures at all time until the program has completed.
6. After the program is complete you should first switch off the router function using the key (and remove it from the slot), then turn off the router head by pushing down the red button on the router head (not the front panel as this will shutdown everything). Remove the protective panel and clean up all dust. You may need to jog the machine clear of your work before trying to detach it from the table.